hydrostat

Century Dictionary and Cyclopedia

1. n. An apparatus of any kind for preventing the explosion of steam-boilers.
2. n. An electrical device for detecting the presence of water, used as a protection against damage to buildings from overflow or leakage.

Wiktionary

1. n. a device that automatically responds to drops in humidity by adding moisture to the air to maintain the humidity at a desired setting, similar to how a thermostat works for temperature.

GNU Webster's 1913

1. n. A contrivance or apparatus to prevent the explosion of steam boilers.
2. n. A device, usually electrical, for indicating or regulating the height of water in a reservoir or receptacle.